It is very important that you clarify with your midwife what information she used to calculate your due date. Pregnancy is usually dated from the first day of the last menstrual period and averages between 279 and 282 days. A convenient method used to estimate the due date is Naegle's rule: to the first day of the last *normal* period add 7 days, subtract 3 months, and add 1 year.

About 8 percent of pregnant women have a small amount of bleeding approximately six weeks after the last period. This is thought to be due to implantation of the fertilized ovum into the endometrium (lining of the womb). This bleeding is often mistaken for a period and can cause confusion regarding the due date.

Pregnancy begins with the fertilization of the ovum. In a women with 28 day menstrual cycles, conception can occur mid-cycle or at approximately day 14 (it can also occur at any time during the cycle).

When planning a pregnancy, a preconception visit with your healthcare provider is recommended. He or she can review your health history, discuss the use of prescription and over-the-counter drugs and stress the use of folic acid in the prevention of birth defects. Folic acid is a B vitamin found in all over the counter multivitamins. Since the neural tube (brain and spine) and many of the baby's other organs begin developing before you miss your period, a daily vitamin is recommended for all women during the childbearing years.

Contact the March of Dimes resource center for more information on folic acid and preconception planning.

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